This invention relates to structural bonding arrangements in aircraft leading edge components that include an ice-protection system.
Known heater mats such as those that are used as part of a de-icing system for a leading edge of an aircraft include a thermoelectric heater element and one or more layers of a dielectric material such as Kapton. The dielectric protects the thermoelectric heater element and can serve to electrically insulate it from a metallic surface (such as an inner surface of a skin of an aircraft leading edge) to which the heater mat is to be applied.
A problem with known heater mats is that they are difficult to apply to portions of an aircraft leading edge structure (e.g. a skin of the leading edge) that are obscured by other parts of the structure (for example, a supporting rib). Known supporting ribs typically include a flanged portion through which attachments such as rivets may pass to fix the rib to the skin of the leading edge. However the flanged portion generally obscures at least a portion of the surface of the skin, inhibiting convenient application of a heater mat to that portion. Although the heater mat may be placed over (on top of) the flanged portion, the flow of heat produced by the heater mat to the skin directly beneath the flanged portion would still be inhibited by the presence flanged portion. Moreover, although a heater mat may be placed in between the skin and the flanged portion, attachment means such as metallic rivets passing through the flange and into the skin would tend to produce short circuits within thermoelectric heater element of the mat.
Conventional means for attaching different parts of an aircraft leading edge structure include rivets (as mentioned above) and adhesive resins. Although known resins may typically be strong enough to adhere a heater mat to part of an aircraft leading edge, they are typically not strong enough to fix together structural features such as a supporting rib and a skin of the leading edge.
Furthermore, the dielectric materials hitherto used in heater mats have limited operating temperatures. The maximum operating temperatures of hitherto used dielectrics limits the amount of heating power known heater mats can produce. Additionally, the limited temperatures that hitherto used dielectrics limits can withstand exacerbate problems associated with the development of “hot spots” in a heater mat (for example due to internal short circuits or other failures), potentially leading to catastrophic failure.
Additionally, the condition of some dielectric materials such as Kapton can deteriorate over time. This can lead to failure of the heater mat on exposure of the thermoelectric heater element to moisture, and/or can lead to short circuiting of the thermoelectric heater element on a metallic surface to which the heater mat is applied.
This invention has been made in consideration of at least some of the problems indicated above.